It is estimated that over half of drug targets are membrane proteins. Detailed knowledge of membrane protein structure (determined using X-ray diffraction of membrane protein crystals) is needed to understand the processes that are driven by these proteins, and to rationally design new molecules that can serve as drug treatments for many diseases. The supply of membrane protein solution for crystallization is limited, and so crystallization trials must be economically miniaturized in order to increase the success rate of crystallization while reducing the cost of each protein structure. This proposal describes a multi-disciplinary research program that aims to develop and validate microfluidic technology enabling rapid and economical crystallization of membrane proteins, performed on nanoliter scale with direct testing of diffraction quality of crystals. The specific aims of the program are to: (1) develop and to validate basic plug-based microfluidic technology for accurate and easy fluid manipulation of the various reagents required for membrane protein crystallization, (2) to use the basic microfluidic technology to develop a preloaded cartridge-based approach to crystallization of membrane proteins, and (3) to broaden the impact of the technology developed by: a) developing preloaded cartridges for the promising new crystallization techniques, b) determining the relationship between traditional- and cartridge-based techniques, c) avoiding the potential for damage in handling of crystals by perfecting in-situ diffraction, and d) disseminating the technology to the membrane protein crystal community though our collaborators (Scripps and Argonne National Labs). These tools will be simple and inexpensive to set up and operate, and available to small laboratories. They will also be compatible with automation and robotics. This technology will have a significant impact on the field of membrane protein crystallization, enabling both individual investigators and large centers to determine X-ray crystal structures of new membrane protein targets rapidly and economically.